The present invention relates to an outboard motor having a structure capable of preventing a cooling water from entering an engine and reducing an engine vibration from transferring the vibration to a hull.
FIG. 6 shows an elevational section of an outboard motor having a general structure. Referring to FIG. 6, an outboard motor 1 is provided with an engine holder 3 formed with an oil pan 2, an engine 4 disposed to an upper portion of the engine holder 3 and a drive shaft housing 5 disposed to a lower portion of the engine holder 3, in an installed state of the outboard motor 1.
In the engine 4, a crank shaft 6 is arranged perpendicularly and an upper end portion of a drive shaft 7 is connected to a lower end portion of the crank shaft 6. The drive shaft 7 extends downward inside a shaft pipe 8 formed on the side of the oil pan 2 and a shaft pipe 9 formed inside the drive shaft housing 5, and the drive shaft 7 operates to drive a propeller 11 through a bevel gear and a propeller shaft, not shown, disposed in a gear case 10 arranged to a lower portion of the drive shaft housing 5.
The outboard motor 1 is generally provided with a water-cooling type cooling device, which acts to pump up such as sea water by a water pump disposed to the lower portion of the drive shaft 7 as a cooling water, which is supplied to the respective elements of the engine 4 through a water pipe 13. In order to prevent the water pump 12 from sucking an air in the shaft pipes 8 and 9, a part of the cooling water is over-flowed into the shaft pipe 9 disposed above the water pump 12. Further, the shaft pipe 9 is formed with a hole 14 communicating with an external portion for the purpose of discharging, through the hole 14, the cooing water over-flowed in the shaft pipe at a time when an inner pressure of the shaft pipe increases. A seal member 15 is disposed at a mating surface between the engine 4 and the oil pan 2, i.e. the upper end portion of the shaft pipe 8 and is adapted to prevent the cooling water from invading into the engine 4.
The outboard motor 1 is mounted to a transom 16a of a hull 16 through clamp brackets 17 and steering brackets 18, and the steering brackets 18 are mounted to the wall section constituting the oil pan 2 of the engine holder 3. With reference to FIG. 7, a pair of upper mounts 19 are fixed to the wall section of the oil pan 2 through elastic members 20 such as rubber. The upper mounts 19 are disposed so as to sandwich the drive shaft 7 from both sides thereof and the steering brackets 18 are fixed to the upper mounts 19 by means of bolts 21, for example.
According to the structure described above, however, when the seal member 15 disposed to the upper end portion of the shaft pipe is damaged, the cooling water in the shaft pipe invades into the engine, causing a troublesome problem.
Furthermore, since the drive shaft near the upper mounts is positioned inside the shaft pipe, it becomes difficult to take much space or volume for the elastic members because of the location of the shaft pipe. Hence, the vibration of the engine may not be sufficiently absorbed and will be transferred to the hull.